1. Field of the Invention
This invention relates to a joint between traveling water screen trays. More specifically, the invention is directed to adjoining transverse members of adjacent screen tray frames and to a flexible seal therebetween.
2. Description of the Prior Art
A traveling water screen removes trash and coarse objects from a stream of water flowing in a water intake channel. Such screens can be equipped with pans for removing aquatic life from the stream, and the aquatic life is returned to the stream at a safe location remote from the screen. The traveling water screen extends transversely of the water intake channel. The screen is formed by a plurality of screen trays that are fastened on opposite sides to the links of long pitch chains that travel in an endless vertical loop about head sprockets and foot sprockets with ascending and descending runs therebetween. Each screen tray has a rectangular frame that is formed by a pair of side members and a pair of transverse members. A screen cloth is attached to the frame for straining the water that flows through the screen.
Water used for cooling purposes at power plants formerly has been passed through woven wire screen cloth having three-eighths inch square openings. Recently, there has been an increased emphasis upon the protection of aquatic life, such as fish larvae and eggs. This necessitates the use of screening media with openings of less than one millimeter wide. Previously acceptable operating clearances between screen trays must be reduced to correspond with the smaller openings in the screening media, but the screen trays must be able to move freely as the long pitch chains travel about the sprockets. Furthermore, the tray frame members should be formed and assembled to economically feasible tolerances. The tray frame members must be strengthened to withstand high differential head loads on the screens. The transverse members of the tray frames must be shaped and arranged to permit the screening surface to be flushed on either the ascending side or the descending side near the top of the vertical loop formed by the traveling water screen.
Some known traveling water screens have transverse seals between adjoining screen tray members. These seals are formed by adjoining transverse members having concentric curved portions that overlap in both vertical and horizontal planes. The transverse members are made of sheet metal, and thus, such seals are limited to economically feasible tolerances for forming and assembling the transverse members. These tolerances would be greater than allowable for the protection of fish larvae and eggs.
Tray to tray contact seals that include a flexible member have been used to provide a more complete seal. Such seals, as previously used, were not suitable for screens with a back wash system because the seals retained debris dislodged from the screen by the back wash.